The film is based on an Aligarh Muslim University professor, who was suspended for allegedly having gay sex, weeks before his retirement in 2010.
S R Siras was later reinstated after Allahabad High Court revoked the suspension. He died the same year.
"The film is based on many such true incidents which are happening in our country for a long time. Marginalisation of people based on religion, caste, gender and sexual orientation is not new. I feel the debate on sexual orientation should be a part of mainstream," Mehta told PTI.
The untitled film, starring Manoj Bajpayee, 45, as the professor and Rajkummar Rao as a journalist, will mark the beginning of Mehta's production company Karma Pictures.
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The director got to know about the incident when a girl, Ishani Banerji, mailed him the story in the beginning of this year. His editor Apurva Asrani is turning writer with the film.
On his decision to cast Manoj, Mehta said he was trying to find a good story to work with the versatile actor.
Mehta is collaborating with Rajkummar, 30, for a third time with this film.
"I can't work without Rajkummar. I see him in every film of mine. He is a part of my family now. I always find a character for him. He is a great actor and one of the best in the new generation. I thought it would be interesting to bring two such performers together," said the director.